Weisskopf Laure, Abou-Mansour Eliane, Fromin Nathalie, Tomasi Nicola, Santelia Diana, Edelkott Iris, Neumann Günter, Aragno Michel, Tabacchi Raffaele, Martinoia Enrico
Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, 8008 Zürich, Switzerland.
Plant Cell Environ. 2006 May;29(5):919-27. doi: 10.1111/j.1365-3040.2005.01473.x.
White lupins (Lupinus albus L.) respond to phosphate deficiency by producing special root structures called cluster roots. These cluster roots secrete large amounts of carboxylates into the rhizosphere, mostly citrate and malate, which act as phosphate solubilizers and enable the plant to grow in soils with sparingly available phosphate. The success and efficiency of such a P-acquisition strategy strongly depends on the persistence and stability of the carboxylates in the soil, a parameter that is influenced to a large extent by biodegradation through rhizosphere bacteria and fungi. In this study, we show that white lupin roots use several mechanisms to reduce microbial growth. The abundance of bacteria associated with cluster roots was decreased at the mature state of the cluster roots, where a burst of organic acid excretion and a drastic pH decrease is observed. Excretion of phenolic compounds, mainly isoflavonoids, induced fungal sporulation, indicating that vegetative growth, and thus potential citrate consumption, is reduced. In addition, the activity of two antifungal cell wall-degrading enzymes, chitinase and glucanase, were highest at the stage preceding the citrate excretion. Therefore, our results suggest that white lupin has developed a complex strategy to reduce microbial degradation of the phosphate-solubilizing agents.
白羽扇豆（Lupinus albus L.）通过产生一种名为簇生根的特殊根系结构来应对磷缺乏。这些簇生根向根际分泌大量羧酸盐，主要是柠檬酸盐和苹果酸盐，它们作为磷的增溶剂，使植物能够在磷有效性低的土壤中生长。这种磷获取策略的成功与效率很大程度上取决于羧酸盐在土壤中的持久性和稳定性，而这一参数在很大程度上受根际细菌和真菌的生物降解影响。在本研究中，我们表明白羽扇豆根系利用多种机制来减少微生物生长。在簇生根成熟状态下，与簇生根相关的细菌丰度降低，此时会观察到有机酸大量分泌以及pH值急剧下降。酚类化合物（主要是异黄酮）的分泌诱导了真菌孢子形成，这表明营养生长以及潜在的柠檬酸盐消耗减少。此外，两种抗真菌细胞壁降解酶——几丁质酶和葡聚糖酶的活性在柠檬酸盐分泌之前的阶段最高。因此，我们的结果表明白羽扇豆已形成一种复杂策略来减少微生物对磷增溶剂的降解。
